|Publication number||US7964497 B2|
|Application number||US 12/163,172|
|Publication date||Jun 21, 2011|
|Filing date||Jun 27, 2008|
|Priority date||Jun 27, 2008|
|Also published as||CN101615591A, EP2139034A1, US20090321933|
|Publication number||12163172, 163172, US 7964497 B2, US 7964497B2, US-B2-7964497, US7964497 B2, US7964497B2|
|Inventors||Fenton R. McFeely, Chih-Chao Yang|
|Original Assignee||International Business Machines Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (23), Non-Patent Citations (3), Classifications (15), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to semiconductor interconnect structures and more particularly, to improved high aspect ratio vias and techniques for the formation thereof.
As the dimensions of multilayer wiring array features continue to shrink, the fabrication of vias is becoming increasingly more difficult. Namely, conventional via fabrication processes are unable to keep up with currently desirable scaled feature sizes.
A problem with this approach is that, as the via width shrinks to below about 80 nm and the aspect (depth/width) ratio becomes larger than about 5:1, the electroplating of the structure begins to fail. As shown in
In an attempt to prevent the above-described overhang occlusion problem, an alternative approach has been devised where instead of sputter depositing a Cu seed layer onto the diffusion barrier layer, a ruthenium (Ru) seed layer is deposited onto the diffusion barrier layer by chemical vapor deposition (CVD), i.e., from a ruthenium carbonyl (Ru3(CO)12) precursor in the presence of excess CO. A Ru seed layer produced in this manner can be conformally deposited and thus does not create a thick overhanging layer, which greatly reduces the problem of void formation in the subsequent Cu electroplating step.
Use of a Ru seed layer, however, has significant drawbacks that arise from the relatively high resistivity of Ru compared to Cu and the chemical inertness of Ru. For example, following electroplating chemical-mechanical polishing (CMP) is typically used to plane the via metal down to the dielectric surface. As a practical matter, five nm is an approximate upper limit for the amount of Ru which can be polished away using a standard Cu polishing slurry. However, the bulk resistivity of Ru is more than four times higher than that of Cu. If only five nm of Ru are deposited, the resistivity of the resulting structure renders electroplating extremely difficult, as voltage drops across the wafer cause unacceptable non-uniformity in the Cu deposition. One could increase the conductivity of the substrate by depositing a thicker layer of Ru, and alleviate this problem, but then the subsequent CMP process would not be possible. One is left with a choice of problems, if the Ru is thick enough to make plating easy, subsequent CMP is not possible with the standard Cu polishing slurry. If the Ru layer is thinned to the point where CMP becomes possible, the substrate is too resistive for uniform plating using standard techniques. Furthermore, even if a method is developed to polish thicker layers of Ru, it would not be a desirable solution. The additional Ru added to facilitate the electroplating process would remain in the vias after CMP, which would reduce the volume available in the vias for Cu, and the resistance of the vias would be significantly increased, degrading performance.
Thus, improved via fabrication processes are needed that can accommodate the most current scaled technology requirements and can consistently produce properly functioning, viable vias.
The present invention provides improved high aspect ratio vias and techniques for the formation thereof. In one aspect of the invention, a method of fabricating a copper plated high aspect ratio via is provided. The method comprises the following steps. A high aspect ratio via is etched in a dielectric layer. A diffusion barrier layer is deposited into the high aspect ratio via and over one or more surfaces of the dielectric layer. A copper layer is deposited over the diffusion barrier layer. A ruthenium layer is deposited over the copper layer. The high aspect ratio via is filled with copper plated onto the ruthenium layer.
In another aspect of the invention, a copper plated high aspect ratio via formed in a dielectric layer is provided. The copper plated high aspect ratio via comprises a high aspect ratio via; a diffusion barrier layer lining the high aspect ratio via and one or more surfaces of the dielectric layer; a copper layer over the diffusion barrier layer; a ruthenium layer over the copper layer; and copper plated onto the ruthenium layer filling the high aspect ratio via to form the copper plated high aspect ratio via.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.
As shown in
As shown in
Ruthenium (Ru) seed layer 250 is then deposited over Cu seed layer 240. Ru seed layer 250 can be deposited using any suitable deposition process, such as CVD or ALD. According to an exemplary embodiment, Ru seed layer 250 is deposited using CVD, i.e., from a ruthenium carbonyl (Ru3(CO)12) precursor in the presence of excess CO. Advantageously, Ru seed layer 250 formed by this highly conformal process is deposited only to a thickness that ensures a continuous coverage on the via sidewalls, and is therefore within limits set by standard chemical-mechanical polishing (CMP) (see description of
As shown in
One advantage of the present Ru-on-Cu bilayer seed layer configuration (for Cu electroplating, see above) is that Cu plated onto Ru exhibits a superior morphology, for example, as compared to Cu plated on a Cu seed layer. Namely, in the lines, larger grains are observed, and in the via, both larger and oriented columnar grains are found. The larger grains improve conductivity, thus improving performance of the vias.
Prior via fabrication techniques also involving a bilayer seed layer employed a Cu-on-Ru configuration. This Cu-on-Ru configuration, however, has several notable disadvantages over the present Ru-on-Cu bilayer configuration. Namely, the Cu-on-Ru configuration does not provide the morphology advantages associated with Cu plating onto Ru, as described above. Further, with the present Ru-on-Cu bilayer configuration, the Cu component of the bilayer can be made thinner than in a Cu-on-Ru configuration, and still remain viable for plating.
By way of example only, both Ru-on-Cu and Cu-on-Ru seed layers were produced on identical via structures, with one nm of Ru on three nm of Cu and with three nm of Cu on one nm of Ru, respectively. Using identical plating conditions it was found that the Ru-on-Cu sample plated successfully (i.e., uniform plating) while the Cu-on-Ru sample did not. The plating of the Cu-on-Ru sample showed the type of gross non-uniformity associated with insufficient conductivity of a substrate.
The difference in the samples may be due to differing degrees of oxidation that the two seed layers incurred upon exposure to the atmosphere. Ru, a noble metal, is much less susceptible to oxidation than Cu. In the Ru-on-Cu structure the Cu is protected from oxidation by the Ru layer thereover, while in the Cu-on-Ru structure the Cu is directly exposed to the atmosphere. The oxidation of the Cu decreases the conductivity of the Cu-on-Ru seed layer making plating more difficult. It is also possible that significant dissolution of Cu oxide may occur in a plating bath, with similar deleterious consequences for the substrate conductivity.
Another advantage of the Ru-on-Cu bilayer configuration is that, when diffusion barrier layer 230 comprises TaN (see above), a Cu/TaN interface results (i.e., between the Ru-on-Cu bilayer seed layer and the diffusion barrier layer). The Cu/TaN interface has been extensively tested and routinely employed in conventional systems.
Although illustrative embodiments of the present invention have been described herein, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be made by one skilled in the art without departing from the scope of the invention.
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|1||Extended European Search Report dated Jun. 2, 2009.|
|2||Japan Office Action dated Oct. 30, 2009.|
|3||Japan Office Action dated Sep. 3, 2009.|
|U.S. Classification||438/627, 438/687, 438/653, 438/643, 257/E21.584|
|International Classification||H01L21/44, H01L21/4763|
|Cooperative Classification||H01L23/53238, H01L2924/0002, H01L2221/1089, H01L21/76843, H01L21/76873|
|European Classification||H01L21/768C3B, H01L21/768C3S2, H01L23/532M1C4|
|Oct 14, 2008||AS||Assignment|
Owner name: INTERNATIONAL BUSINESS MACHINES CORPORATION, NEW Y
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Owner name: INTERNATIONAL BUSINESS MACHINES CORPORATION, NEW Y
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